From e2bf3e6ecaff79c5479682da2dc7b2035e52c5b8 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Thu, 10 Dec 2015 18:21:41 +0100 Subject: clocksource: Mmio: remove artificial 32bit limitation The EP93xx is registering a clocksource of 40 bits with clocksource_mmio_init() but this is not working because of this artificial limitation. It works fine to lift the uppe limit to 64 bits, and since cycle_t is u64, it should intuitively have been like that from the beginning. Fixes: 000bc17817bf "ARM: ep93xx: switch to GENERIC_CLOCKEVENTS" Reported-by: Alexander Sverdlin Signed-off-by: Linus Walleij Cc: Daniel Lezcano Link: http://lkml.kernel.org/r/1449768101-6879-1-git-send-email-linus.walleij@linaro.org Signed-off-by: Thomas Gleixner --- drivers/clocksource/mmio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/clocksource') diff --git a/drivers/clocksource/mmio.c b/drivers/clocksource/mmio.c index 1593ade2a815..c4f7d7a9b689 100644 --- a/drivers/clocksource/mmio.c +++ b/drivers/clocksource/mmio.c @@ -55,7 +55,7 @@ int __init clocksource_mmio_init(void __iomem *base, const char *name, { struct clocksource_mmio *cs; - if (bits > 32 || bits < 16) + if (bits > 64 || bits < 16) return -EINVAL; cs = kzalloc(sizeof(struct clocksource_mmio), GFP_KERNEL); -- cgit v1.2.3 From f9eccf24615672896dc13251410c3f2f33a14f95 Mon Sep 17 00:00:00 2001 From: Roman Volkov Date: Fri, 1 Jan 2016 16:24:41 +0300 Subject: clocksource/drivers/vt8500: Increase the minimum delta The vt8500 clocksource driver declares itself as capable to handle the minimum delay of 4 cycles by passing the value into clockevents_config_and_register(). The vt8500_timer_set_next_event() requires the passed cycles value to be at least 16. The impact is that userspace hangs in nanosleep() calls with small delay intervals. This problem is reproducible in Linux 4.2 starting from: c6eb3f70d448 ('hrtimer: Get rid of hrtimer softirq') From Russell King, more detailed explanation: "It's a speciality of the StrongARM/PXA hardware. It takes a certain number of OSCR cycles for the value written to hit the compare registers. So, if a very small delta is written (eg, the compare register is written with a value of OSCR + 1), the OSCR will have incremented past this value before it hits the underlying hardware. The result is, that you end up waiting a very long time for the OSCR to wrap before the event fires. So, we introduce a check in set_next_event() to detect this and return -ETIME if the calculated delta is too small, which causes the generic clockevents code to retry after adding the min_delta specified in clockevents_config_and_register() to the current time value. min_delta must be sufficient that we don't re-trip the -ETIME check - if we do, we will return -ETIME, forward the next event time, try to set it, return -ETIME again, and basically lock the system up. So, min_delta must be larger than the check inside set_next_event(). A factor of two was chosen to ensure that this situation would never occur. The PXA code worked on PXA systems for years, and I'd suggest no one changes this mechanism without access to a wide range of PXA systems, otherwise they're risking breakage." Cc: stable@vger.kernel.org Cc: Russell King Acked-by: Alexey Charkov Signed-off-by: Roman Volkov Signed-off-by: Daniel Lezcano --- drivers/clocksource/vt8500_timer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'drivers/clocksource') diff --git a/drivers/clocksource/vt8500_timer.c b/drivers/clocksource/vt8500_timer.c index a92e94b40b5b..dfc3bb410b00 100644 --- a/drivers/clocksource/vt8500_timer.c +++ b/drivers/clocksource/vt8500_timer.c @@ -50,6 +50,8 @@ #define msecs_to_loops(t) (loops_per_jiffy / 1000 * HZ * t) +#define MIN_OSCR_DELTA 16 + static void __iomem *regbase; static cycle_t vt8500_timer_read(struct clocksource *cs) @@ -80,7 +82,7 @@ static int vt8500_timer_set_next_event(unsigned long cycles, cpu_relax(); writel((unsigned long)alarm, regbase + TIMER_MATCH_VAL); - if ((signed)(alarm - clocksource.read(&clocksource)) <= 16) + if ((signed)(alarm - clocksource.read(&clocksource)) <= MIN_OSCR_DELTA) return -ETIME; writel(1, regbase + TIMER_IER_VAL); @@ -151,7 +153,7 @@ static void __init vt8500_timer_init(struct device_node *np) pr_err("%s: setup_irq failed for %s\n", __func__, clockevent.name); clockevents_config_and_register(&clockevent, VT8500_TIMER_HZ, - 4, 0xf0000000); + MIN_OSCR_DELTA * 2, 0xf0000000); } CLOCKSOURCE_OF_DECLARE(vt8500, "via,vt8500-timer", vt8500_timer_init); -- cgit v1.2.3